Method of producing alpha polished surface on granite blocks



Patented July 26, 192 7.

UNITED STATES PATENT OFFICE.

ELROY ALBERT C HASE, OF NORTHFIELD, VERMO N'I.

METHOD OF PRODUCING A POLISHED SURFACE 0N GRANITE BLOCKS.

Io Drawing. Application flled'May 24,

This invention relates to an improved method or process of producing a highly olished surface on granite blocks of varying sizes.

It is the general object of my invention to provide a method or process by which a better surface ma be attained, together with a very materia reduction both in the labor cost and in the time required to complete the polishing operation.

With this eneral object in view, my invention inclu es a series of successive operations upon the blocks to be polished,- which will be hereinafter described and more particularly pointed out in the appended claims.

For a clear understanding of my improved process, a brief statement is necessary of the method by which a lished surface has been heretofore produce upon granite blocks. It has been the revious practice to assemble a number of different blocks on a single bed surrounded b raised sidewalls, the spaces between the b ocks being filled in with plaster so that the bed might present a continuous surface. 'Theassembled' blocks were then subjected to a so-called ironing operation in which steel shot was forced against the high spots of the blocks by means of scroll Wheels which picked up the shot at their outer edges and worked it toward the center of the wheel. This process broke down or crushed the high spots on the different blocks and was continued until all of the blocks were brought to a comparatively smooth surface in a single plane. The entire bed was then cleaned and all shot and steel particles were carefully removed.

A coarse grinding operation was then carried out with a coarse grade of emery or carborundum which was fed to ring wheels having smooth continuous sides and bottom faces and of less diameter than the width of the bed. The grinding material was manually applied to the rings by the use of a paddle or similar device and the grinding process was continued until the ironing marks were removed. The coarser portion of the grindingmaterial was then removed and the intermediate polishing or finingup step of the-process was carried out with a reduced amount of grinding material, the grain of which became gradually finer as it was worn down in the grinding operation.

After the grinding and fining-up or polishing was completed, the grinding wheel was removed and the bed was again cleaned,

With my improvedprocess, the operation iscommonly carried out on individual blocks of stone which preferably have their fiat faces formed by a granite saw such as has been heretofore patented b me. The surfaces are thus approximate y plane and accurate and the improvements which I have devised in the grinding rocess enable me to entirely omit the ironing operation. If,

however, certain blocks are found to have faces which are too irregular for the coarse grinding operation, a preliminary ironing operation may be performed thereon, preferably using the improved type of ironing wheel which is shown in my prior Patent No. 1,455,477, issued May 15, 1923.

The sawed or ironed stone is supportedin fixed position in a suitable box or trough and is first subjected to a'coarse grinding operation by a ring wheel or scroll of special form, such as is shown, for instance, in my prior applications, Serial Nos. 536,533 and 552,278, fi ed respecti ely February 14, 1922 and April 13, 1992. In each of these constructions, the inner faces of the grinding rings or scrolls are provided with pockets of special design which act to receive and store the grinding material as it Works gradually outward from a central feed opening. The pockets feed the abrasive directly under the grinding surfaces of the wheels.

This storage capacity of the wheels greatly assists me to dispense with the formation of the large continuous bed which has been heretofore required and to use a wheel of greater diameter than the width of the block, as I find that the abrasive is retained in the pockets when portions of the wheel revolve beyond the edges of the stone, and that the abrasive is thus held in position so that each portion of the wheel'will resume its grind- The ring wheels used in the old process entirely lacked this storage features and merely swept the abrasive oil" of the edges of the stone if allowed to revolve beyond the edge thereof.

I preferably provide an automatic feed of abrasive to the center of the rinding wheel, from which point the materia works gradually outward toward the edges, bringing the surface rapidly to a smooth condition. This center feed permits increased speed of rotation and the increased speed, together with the storage effect of the pockets, reduces the time of the grinding operation to a small fraction of the time previously required for ironing and coarse grinding. This reduction in time is also partly due to the fact that the old form of Wheels with hand feed ran for aconsiderable portion of the time practically idle, as it was almost impossible for the operator to maintain at all times an even supply of abrasive under the grinding faces.

After the coarse grinding operation is completed, the stone is preferably removed entirely from the coarse grinding machine and is placed in a second machine for the intermediate polishing or fining-up process. No careful cleaning of the grinding machine is required, as it uses the same grade of material continuously. For this second operation, I may desirably use a wheel having a plurality of concentric plain rings secured together by radial arms which also connect the rings to a driving head. the wheel being of lighter construction than the coarse grinding wheel and preferably having no pockets in its grinding surface. An improved form of wheel for this intermediate or polishing operation is shown in my copendin application, Serial No. 599,037, filed November 4, 1922.

In carrying out this intermediate polishing, the upper surface of the stone is moistened and a certain grade of fine powdered abrasive is fed to the wheel. The wheel is then rotated over the stone, the motion of the wheel preferably being such that the wheel advances bodily tpward that edge of the wheel which is leaving the edge of the stone, thus carrying the coarser particles of the material over the edge. Water is allowed to drop on the stone in sufficient amounts to keep the polishing material in a pastelike form.

After perhaps five minutes, a finer grade of polishing material is applied to the stone and the wheel is run with this material for another short period, after which a still finer grade is substituted, this process being continued until the desired polish is pro duced.

It is found that this'process of substituting successive grades 0 fine polishing material saves a great deal of time when compared with the old process in which the original coarse abrasive was gradually worn down by grinding contact with the stone until it was sufficiently fine to give the desired finish. This old process frequently required some four or five hours for the intermediate or fining-up step, whereas similar or better results can be obtained by my improved process in from twenty minutes to half an hour. The certainty of the results is also much improved, as a certain definite grade of polishing material can be supplied at each step in the process, instead of depending upon the indefinite and uncertain wearing out of the original abrasive, as previously employed.

When a wheel of this sort is used, it is desirable that the wheel be larger in diameter than the width of the block so that it may be moved back and forth in a straight line over the block to act on all portions thereof. Such movement may be produced automatically, enabling one man to attend several such machines instead of giving his entire personal attention to a single polishing wheel.

After the fining-up operation, the final butling operation is carried out by means of wheels having felt bufiing surfaces and using a fine olishing powder, such as oxide of zinc. The time required for the buffing operation has also been very materially reduced, due

in part to the fact that the blocks of stone are not bedded in plaster and consequently there is no plaster to mix with the polishing powder and reduce its efiiciency. The time is also reduced by the use of the improved form of buffing wheel shown in my prior application, Serial No. 536,532,.filed February 14, 1922, in which the bufiing surface is made up of a plurality of separately yield able cushion members or projections. This construction permits. the wheel to adapt itself much more readily to the surface on which it works, so that it will quickly reduce a uniform olish upon a surface w ich may vary slight y from a true plane.

As a result of the use of my improved coarse grinding, intermediate, and butiing wheels, together with the improved method or process in which the wheels are utilized, the work of producing a polished surface on granite blocks has been made very largely automatic and both the time required and the cost of labor have been greatly reduced when compared with the results attained by the old process.

A very important result arises from the omission of the ironing operation. Certain kinds of granite contain mica which is crushed by the steel shot to a point below the level of the harder uartzand feldspar in the granite. It was a most impossible by the 01d process to remove these mica depressions from the surface and obtain an unbroken polish. With my new process, the ironing izo is omitted and these depressions are not formed. My improved coarse grinding wheels with center feed are also able to use a coarser abrasive than the old ring wheels and to use it much. more effectively, reatly reducing the time required to pro uce a given result. v f

The center feed of this wheel also makes possible a higher speed of rotation than could be used with the old paddle feed and this higherspeed in turn increases the storage capacity of the wheel by retaining a por tion of the abrasive against the inner faces of the rings or scrolls, from which it flows graduallyto the pockets and thence to the proximately plane regular surface coextensiye with one face thereof, in subjecting said single granite block as a complete unit separately and successively to a coarse grinding operation, and a finlng-up operation over said entire surface, said coarse grinding operation being carried out in a machine especially adapted for coarse grinding and said fining-up operation being different machine especially adapted for fining-up, said graniteblock being moved from the first machine to the second machine after the coarse grinding operation thereon, and each granite block being individually and firmly supported as a separate unit in each machine and throughout each operation thereon, and the edgesof said block being at all times freefrom embedding material.

' 2. The method of producin a polished V surface on granite blocks whic consists in providing each granite block with an approximately plane regular Surface co-extensive with one face thereof, in subjecting said single granite block as a complete unit separately and successivel to a coarse grinding, a fining-up and a bu ng operation over said entire surface, and in moving each blockto a successive machine between each two successive o erations, each machine being espe-' cially a apted to its particular operation, and each block being individually and firmly supported as a unit in each machine and throughout each opieration thereon, and the edges of each bloc being at all times free from embedding material.

3. The method of roducin a polished surface on a granite b ock whic consists in providing an approximately plane unfincarried out in aished surface on a block of granite, firmly supporting said block as a complete and separate unit free from embedding material about its edges, smoothing said unfinished surface by grinding with a coarse abrasive, thereafter fining-up said surface, in a series of separate steps, using separate and successive applications of fresh and successive- 1y finer polishing abrasives of definite grades, each grade of abrasive remaining on the block for a relatively short run only, and the greater part of each grade of abrasive passing from the block while it is of substantially its original grade, and finally buffing thepolished surface of the block.

4. The method of producing a polished surface on a granite block which consists in providing an approximately plain unfinished surface on a block of granite, smoothing said unfinished surface by inding with a coarse abrasive, thereafter r l ing-up said surface with a relative finer abrasive of a definite and substantially uniform grade until a texture of surface is produced upon which said abrasive will not have further substantial smoothing effect while it retains substantially its original grade, repeating said fining-up operation with an abrasive of still finer and substantially uniform grade to a corresponding condition of surface smoothness, and continuing said fining-u operations and said changing to successively finer grades of abrasive until the desired smoothness lof surface is attained.

5. The method of producing apolished surface on a granite block which consists in providing an approximately plain unfinished surface on a block of granite, firmly sup porting said'block as a complete and separate unit free from embedding material about its edges, smoothing said unfinished surface by grinding with a coarse abrasive, thereafter fining-up said surface with a relatively finer abrasive of a definite and substantially uniform grade until said grade of abrasive has no further substantial smoothing effect on said surface, repeating said fining-up operation with a still finer abrasive of S11 stantially uniform grade to a corresponding condition of surface smoothness, and continuing said fining-up operations, using successively finer but substantially uniform grades of abrasive until the desired smoothness of surface is attained.

6. The method of fining-up a block of granite which consists in supporting the block in fixed position with its edges free from embedding material, supplying water and abrasive thereto, rapidly rota-ting a fining-up wheel thereover and in contact therewith, and moving said wheel bodily over said block with a portion thereof projecting beyond the edge of the block, the movement being in such a direction that the projecting portion of the wheel at its advanced edge is leaving the edge of the block duced to the normal size of said coarse abrasive, removing said'coarseeabrasive. then reducing by an abrasive of substantially uniform finer ade, discontinuing such reduction when t e asperities are reduced to the normal size of saidfiner abrasive, removing said finer abrasive at said stage, and so on until the desired finish be attained.

In testimony whereof I have hereunto affixed my signature.

' ELROY ALBERT CHASE. 

